Hirt Supernatents for Cloning Viral DNA

I am planning to try to clone the episomal form of a retrovirus
using lambda Zap II and a site I expect to be present in the
pol gene. My last efforts on this front flopped.
Does anyone have a protocol for Hirt supernatent preps that
they would recommend? The only paper I have that talks about
this in any detail is the one from Hirt himself (think he
was trying to study T. rex viruses :-) ).
Thanks!
Brian